With the development of electronic equipments, semiconductor devices are widely used in various switching converters. For example, a step-down synchronous switching converter has an input terminal, a high-side switch and a low-side synchronous switch coupled between the input terminal and a system ground, wherein the high-side switch and the low-side synchronous switch are both semiconductor devices. The step-down synchronous switching converter is configured to convert an input voltage to a pulse signal according to a duty ratio and generate a stable DC output voltage via an output filter circuit, wherein the duty ratio is controlled by the high-side switch and the low-side synchronous switch. However, turn on losses of the low-side synchronous switch are large due to a high forward voltage of its body diode, and a slow reverse recovery of the body diode further increases its dynamic losses, so it's difficult to improve the step-down synchronous switching converter's efficiency.